Tracy wrote:

My 5" round inlet for the radiator looks ridiculously small compared to yours but so far it is cooling the 20B OK. 

 

Now that sort of boggles my mind as it seems to violate the laws of physics. Let’s just take a modest climb power of, say; 225 hp.  At that power, the energy going into the coolant is about 6000 Btu/min.  In order to remove that amount of heat, at a typical air temp increase of 75 degrees; takes about 4000 cfm air flow.  A 5” dia inlet is 0.14 sq feet, meaning an average inlet velocity about 29,000 ft/min, or 330 mph.  Even at 100 air temp increase (unlikely on a 90F day) it’s 250 mph.  And I’m guessing your climb speed is half that.  Similar math suggests you’d be limited to a steady state (cruise) power of about 50%.

 

Of course, being a pusher driver, I think of inlet air speeds in terms of the speed of the airplane.  So does the fact that the inlet is behind prop give a much higher effective inlet velocity?  I’ve been thinking that the turbulence in the prop wash would negate a good portion of the extra mean air velocity because of reduced inlet effectiveness.

 

It will be interesting to know how it works out on a hot day.

 

Great that you have your 20B in the air and working well.

 

Merry Christmas and Happy New Year to all.

 

Al G